>$image->URL should call $image->getURL(), which gives you a relative link in 2.3 - so not sure why this fails...

Well yeah, that is indeed what it does.. ;-) But in 2.2.3 , it returned an absolute link .. I think it should be noted in the upgrade-documentation that this is going to happen , because it took me quite some time to figure out why my site got killed.. That is all.. ;-)